if __name__ == '__main__':
    l = [1, 2, 3, 4, 5, 6, 7, 8, 9]

    # 将列表中所有的数值都乘以 2
    # print(l * 2)
    result = []
    for i in l:
        result.append(i * 2)
    print(result)

    result = [i * 2 for i in l]
    print(result)

    result = list(map(lambda i: i * 2, l))
    print(result)
